Hydrocarbon coking apparatus



April 27, 1954 E. s. Pl-:TTYJoHN 2,676,913

HYDROCARBON COKING APPARATUS Filed Feb. 13, 1952 @www Patented Apr. 27, 1954 UNI-TED- STATES PATENT OFFICE HYDROGARBON- COKING APPARATUS Elmore. S. Pettyjohn, Evanston, Ill., assigner to Institute of Gas Technology, Chicago, Ill., a corporation of Illinois ApplicatiunFebruai-y 13, 1952, Serial No. 271,316

3 Claims. l'

This invention. relates to: method and apparatus for producing` both coke and. high heating valuey oil gas (700. to 1500 and preferably from 9;)10toy 1100 or 120013. t. u./S. C. F.) from residual o s.y

The term residual petroleum oils.V is herein employed by Way of a distinction from. distillate petroleum oils and refers. to: liquid petroleum oils or fractions of such. oilscharacterized by a substantial Conradsoni carbon residue, say, 2 or more per cent by Weight. In. general these oils are characterized by aratio of carbon4 to hydrogen of. 6.5 or higher. Examples of residual petroleum oils. are Nos. 5` and 6 fuel oils, Bunker C oil, Vheavy gas. oil, heavy catalytic cracker residues, and cycle iuelV oils.

When residuall oils are cracked by being passed, in vapor form, through a hotV tube to generate a high heating value. fuel. gas, other products than fuel gas are also formed, including carbon and tar (made up.l inpartby-light oils). Typically, a gallonr cik residual oil may yield, say, 4. pounds of. gas about 13/1, pounds of carbon, and about 2.1/2 pounds of tar. More than one-half of the tar may consistof pitch..

It is conventional to. produce an oil gas. ofrelaf tively high heating. value by thermally cracking residual oils in vaporized. form in an atmosphere of steam. On such thermal cracking. ofthe indicated petroleum. oils, carbon. is deposited inthe space Where cracking` is. effected in an. amount requiring frequent removaL. as by burning, if cracking is to be continued.y in the same. space. To handle such cracking, apparatus has heretofore been used comprising. a generator. in which cracking is eiected, and. a super-heater in Which the. oil gas formed. in the generator is. cracked further. This apparatus is operated' by alternately (l) spraying, oil and. introducing air at ambient temperature directly into the generator and there burning the oil to remove carbon deposited. in. the generator and superheater and to raise the generator and' superheater to cracking temperatures and (2') spraying. oil and introducing steam' into the generator after the carbon has been removed and the generator and superheater have been. raised to cracking temperatures.v This isY a rcyclic non-regenerative process.

By way of an. improvement over the` above described cyclic. process including an. oil cracking (or make) step andan oil and carbon burning (or heating. or blasting) step, it has been proposed to provide apparatus including twol left and right generator-superheater pairs: end. a conduit connecting the two generators, for use in a regenerative, cyclic process including two cracking or make steps or periods and two burning or blast' steps or periods. More particularly, if a make period has just been terminated in the rig-ht generator-superheater, air is forced into and through the right generator-superheater for flow into thev generator of the left pair Where the air (then preheated by heat exchange and by combustion of carbon deposited during the make inthe right generator-superheater) Supports the combustion of the oil sprayed into the generator of the left pair, heating the generator and superheater of the left pair to cracking temperature. Oil is next cracked in the left generator-superheater inan atmosphere' of steam. Next the right generator-superheater is heated by forcing air through the left generator-superheater intothe'generator of the right pair Where the air (now preheated by heat exchange and by combustion of carbon deposited during the make in the left generator-superheater) supports .the combustion of oil sprayed into the generator of the right pair. Finally, oil is cracked in the right generator-superheater in an atmosphere of steam- With respect tofuel consumption for maintaining cracking temperature, the. above-noted regenerative four step or period process carried out in two connected generator-superheater pairs is more economical than the above noted nonregenerative two step or period process carried out ina single generator-superheater pair. But the oil. gases produced by the two processes are identical in composition and burning characteristics. As a matter of fact, the composition of the oil gas formed by these and other conventional cracking processes is fixed` by the heating value of the gas produced, being independent of the nature ofy the oil being cracked and of the residencetime. I have ascertained the relation between compositionv and Vlocating value of. oil gases. produced by conventional cracking methods bysubjecting various petroleum oils (including among others, diesel oil, 37.3 A. P. I., 0 weight per cent Conradson carbon residue, C/H=6.39; heavy gas oil, 22.2 A; P. l., 6 weight per cent ConradsonV carbon residue, C/H=7.05; and

YBunker C fuel oil, 9.9 A. P. 1., 11 weight per cent Conradson carbon residue, CHI-:8:51) to thermal cracking at temperatures ranging from 1350 to ()o F., residence times ranging from 1 tov5. seconds, and a partial pressure oi oil gasV ranging from 0:3 to. 0.9 atmosphere. Thefvalue Y u obtained under allfthese conditions from the varif 3 ous oils show that the composition of the oil gas is a function of the heating value of the oil gas, as tabulated:

None of the above tabulated gases are completely interchangeable with natural gas, among other reasons because of their low contents of paraffns and their high contents of unsaturates which, as I have found, confer on these gases burning characteristics entirely different from those of natural gas. Reference is made to the copending application of myself and Henry R. Linden entitled Fuel Gas Interchangeable with Natural Gas and Method of Making the Same for a more complete discussion of the composition of gases interchangeable with natural gas. It is suiiicient, for the purposes of the present application, to state that the above-tabulated gases can be blended with natural gas only to the extent of possibly 20% or 50%, if the resulting gas mixture is to be sent out for use in appliances adjusted for burning natural gas.

In the above noted conventional cracking methods, the carbon deposited in the course of the cracking is burned, to furnish a large part of the heat required for the cracking step. One reason for burning this carbon is the fact that the carbon is deposited in a form resembling lamp black, in which form the carbon is chiefly valuable only as a fuel. The same applies to the value of the pitch which forms the bulk of the tar obtained in the course of such thermal cracking. Further, to recover the heating values of the carbon and the pitch, it is practically almost necessary to burn these materials in the locality where they are produced. In other words, these materials, and particularly the carbon, could not conveniently be transported to other localities for burning in combustion devices such as steam boilers, for the purpose of recovering the heating values thereof.

Residual oils have also been subjected in liquid form to high temperature coking processes wherein the carbon and the pitch are in the form of coke. In some of the high temperature coking processes presently employed for the coking of heavy oils, a pool of oil is` poured on the floor of a distillation chamber heated from below by the combustion of fuel in subjacentflues, the heat required for carbonization being conducted upwardly through said oor. After a first pool of oil has been coked, a second pool of oil is poured onto the coke formed from the first pool. The heat required for carbonization of the second pool is supplied to the pool through the floor of the carbonization chamber and through the rst layer of coke formed from the first pool. This process is repeated until a layer of coke of suitable thickness has been formed on the floor of the chamber. With each successive layer of cake formed, the temperature inside the iiues is progressively raised so that each layer of coke below the uppermost layer is subjected to increasingly higher temperatures for increasingly longer periods of time. As a result, the various layers of coke formed on the'bottom of the chamber are distinguished by widely variant characteristics, as are also the gaseous products obtained in the coking of the various pools of oil.

It has, therefore, been proposed to eiTect transmission of heat to a layer of oil or the like to be carbonized by downward radiation from a source of heat arranged at or near the top of a distillation chamber. However, with such an arrangement, the gases generated during destructive distillation rise and contact said source of heat, being cracked or carbonized with resultant deposition of carbon on the source of heat. In the destructive distillation of heavy oils or the like involving transmission of heat by radiation from above, the removal of carbon deposits from the source of radiant heat has therefore presented a diiilcult problem.

It is, therefore, an important object of the present invention to provide method and apparatus for thermally cracking residual petroleum oils in liquid vform to produce both coke of uniform and consistent characteristics and a high heating value fuel gas more completely interchangeable or even absolutely interchangeable with natural gas, as compared with conventional high heating value oil gas.

Other and further objects and features of the present invention will become apparent from the following description and appended claims as illustrated by the accompanying drawings showing, diagrammatically and by Way of examples, apparatus` according to the present invention.

Figure l is a transverse cross sectional View, with parts shown in elevation, of a furnace according to the present invention; and

Figure 2 is a fragmentary longitudinal vertical cross sectional View taken along the line 2-2 of Figure 2.

My novel apparatus and method for thermally cracking residual oils in liquid form involves the transmission of heat to the liquid being cracked from above by radiation from hollow bodies supplied with air and fuel for internal combustion in said bodies.4 The latter are constructed of silicon carbide (Carborundum) and are able to resist temperatures as high as 2500 to 2600 F. or higher. Further, these bodies, according to my invention, are porous or permeable to gas, so that any carbon deposited on the outside of the bodies can be removed from time to time by forcing the gas outwardly through the porous or permeable bodies. If desired, outward now of gas through the porous or permeable bodies can be maintained constantly, for preventing deposition on the porous bodies of carbon formed on cracking of the distillate. The actual temperature prevailing in the cracking step is about 1200" F. or higher and. suitably between i400 and 1800" F. At these temperatures, the products obtained are a rather large amount of high heating value oil gas, a relatively small amount of liquid distillate containing a relatively large proportion of aromatics, and a dry coke containing a relatively small amount of volatile matter, for instance, as little as 1.5%. In the cracking step, the oil gas and the vapor (of the distillate) are exposedV to the heat in the furnace for a relatively short time, while the coke is exposed to the heat for a relatively long time, whereby the constituents of the vola-tile matter in the coke are cracked, to leave the above dry coke.

' lIhe oil gas 'generated in the above-described cracking step is characterized by a composition dependent upon the heating value of the oil gas ka valved conduit 21.

furnace I the tube Yli'I discharges combustion f as tabulated hereinabove. .But due to the short residence vtime ofthe gas within the above-'mentioned apparatus for Icracking the residual oils, ythe gas will ordinarily have a heating value in excess of 1200 B. t. u./S. C. F. This gas lmay be converted to a fuel gas absolutely interchangeable with natural gas by further cracking at 1350 to 1700 F., a pressure of from 1'to'5 atmospheres and a residence time of 11/2 to 10 vseconds, followed by vautohydrogenation effected by contacting the Ygas with 'a conventional hydrogenation catalyst at a temperature of from .500 to 800 F. and a `space velocity of from 100 to 1000 cubic feet per cubic foot of catalyst volume per hour.

Referring now'to Figures vl and V2, the ,reference ynumeral I0 designates generally a cracking furvteniperature byV means of heat radiating burner tubes l'l piercing the side walls. Oil to be coked 2 is injected into the -coking chamber through nozzles 20 extending through the side walls.

The tubes I'Iare made of carborundum and are sufficiently porous or permeable to permit outward gas iiow therethrough. if desired, these t tubes may be made up in sections. A fluid fuel may be supplied to one end of the tube I'I y(outside the left side lof the furnace I0) through On the Yright side of the gas into a downwardly and then inwardly extending .tube i3 which in `turn discharges into one of a pluralityof Atransverse spaced channels i9 formed within the floor I2 of the furnace I0.

Thesefchannels finally discharge the combustion i gas into a stack Zi for venting to the atmosphere.

Air under pressure is supplied from a conduit 22 through a plurality of valve'd pipes 23 each discharging air into one of a plurality of transverse spaced channels 2d formed within the licor I2 ofthe furnace le and extending between the channels I9. Each of the channelsll supplies air (pre-heated by transfer of heat from combustion gas through the walls separating the chan-V nels IQ and 2li) to one ofthe tubes I'I.

Inl operation of the furnace I0 shown in Figures l and 2, a thin layer of granularor nely divided coke of kthe type obtained bythe operation of .said furnace Visinitially spread over the floor I2 of the chamber Il to form a Zone of cleavage between the cokesubsequently produced Ain the furnace and the floor of the furnace, whereby the removal of thecpke from the chamber at the end ofi-the operating cycle is facilitated. The chamber il is next raised to the de 1 sired temperature -(abc've 1200??. and preferably Vfrom 14:0@ F. tol800 F. -in the coking of petroluem still residues) by combustion of the required amount of fuel and air in the combustion tubes il. r Apredetermined amount Yof residual oil is nextintrodueed into the chamber Y II 'through the nozzles 2d' to `form avr'elatively shallow 'pool' onjth'e floor l2 of the chamber where the oil remains until coked by the heat radiated from the combustion tubes Il. When Vthese gases and vapors.

the first charge has been coked to Aform a laye'r of coke from 1A" to 1' thick, a second ycharge of substantially the same quantity as the first charge is admitted to the chamber II to form a second pool on top of kthe coke formed'from the first charge. This operation Vis repeated with as many subsequent charges of material as is necessary to form a slab of coke .of desired thickness, say, from 1" kto 6". In this slab of coke, each layer yis formed under substantially identical temperature conditions maintained for substantially the same length of time. The slab is, therefore, of uniform quality throughout.

As each pool of residue or tar or the like is being coked, the gases and vapors then generated rise from the pool towards the roof I4 of vthe chamber ll, come in contact with the surfaces of the tubes `II heated by internal combustion :and are cracked on these surfaces to form a layer of coke on the tube surfaces. This layer of coke, if permitted to remain on the tubes, would act as an insulator with the result that the temperature of the chamber would be lowered if the temperature is maintained constant within the combustion tubes, or the internal combustion temperatures would have toY be raised to maintain a constant chamber temperature. In order to maintain a uniform coking temperature withoutV any necessity for raising the internal combustion tube temperature, the coke is periodically cracked off from thef'combustion tubes .I'I by periodically flowing a gas through the tubes I1 at suiicient pressure to cause outward gas ow through the tube walls. The rate of -outward vgas flow' is controlled so that carbon deposited Von the tubes will be 'peeledoif The coke peeled olf from the tubes `I'I falls on top ofthe layer being coked and is incorporated in the nall slab of coke by the colring of a subsequent charge of oil or the like.V The gas thus utilized for removing deposits of carbon may `be combustion gas or may be a calor-iiic gas or vapor that will not dilute the gas produced on destructive distillation so as to reduce ythe caloric value of the latter.

If desired, the pressure within the tubes I'I may at all times bemaintained high'enough to bring vabout constant outward gas flow through the tubes, for preventing the adherence to the tube of carbon formed on cracking of gases or vapors generategfrom the oil being cracked.

In the event that the tubes I1 are cleaned intermittently in the manner described, the frequency of such cleaning is determined by the rate of formation vof gases and vapors contacting the vtubes and on the coke forming characteristics of Such intermittent cleaningcan becarried out'automatical-ly by any suitable means, for instance, thermostatic Vmeans controlled by the'furnace temperature, by thek temperature of the gases discharged from the tube -II into the `stack ZI .or by any-other suitable glmeans, so that the desired chamber temperature rsuitable conduit, Ysuch as thatV indicated at vlli.

Thesegases and vapors are maintained at a tem- :perature of from 1350 F. to 1700 F. for from 1% -to `5 atmospheres.

:to 10 seconds in the next succeeding vapor phase cracking step. The pressure may range from 1 Since these gases and vapors are hot when discharged from the furnace I0, very little additional heat is consumed in the further cracking thereof.

The above noted gas phase cracking step is carried out principally to reduce the oil gas content of higher illuminants (particularly clenes other than ethylene), which may range, say, from 5% to 18%. These higher illuminante when thus cracked in vapor form yield a carbon deposit within Whatever vessel is employed for the vapor phase cracking step. If, as may be done, the vapor phase cracking is carried out in a tube heated externally (if necessary) to maintain the above-noted cracking temperature, the carbon deposited in such a cracking tube may be returned to the furnace IG, for instance, to furnish the ycarbon layer initially deposited on the furnace furnace i0 and wetted with the oil charged to the furnace, is incorporated with the coke formed in the furnace, being bonded together by the 'heavy carbonaceous constituents of the oil cracked in the furnace.

No particular showing in the drawings, nor any `further discussion in this specification is believed required in connection with the above noted vapor phase cracking step as carried out in a heated tube, since such a procedure, in and by itself, is Well within the skill of those versed in the art, in view of the preceding disclosure. It may be noted, however, that relatively small amounts of carbon are deposited from the gas being cracked so that this vapor phase cracking step ordinarily can be carried out continuously (without interruption for removal of deposited carbon) for as long a period of time as may be required between initiation of cracking in the furnace I0 and termination of cracking in the furnace l0 for removal of coke formed therein.

The oil gasl obtained after said vapor phase cracking may be `rendered absolutely intere changeable (if not so interchangeable) with natural gas by catalytic autohydrogenation. For

this purpose, the gas is first passed through a condenser (to remove condensable oils) and thereafter over a hydrogenation catalyst. To secure such a gas absolutely interchangeable with natural gas, the catalyst temperature is maintained within the range of from 500 F. to 800 F'. and the space Velocity is maintained within the range of from 100 to 1000 cubic feet per cubic foot of catalyst volume per hour. The autohydrogenation can conveniently be carried outv at atmospheric pressure, but somewhat better results are obtained at superatmospheric pressure. Any catalyst suitable for the hydrogenation of unsaturated hydrocarbons may be used, for instance, iron, nickel, cobalt, the oxides of these metals, platinum, palladium, vanadium and its oxide, and the oxides of chromium and molybdenum. By way of an example of such autohydrogenation, we `have treated the above tabulated make gas (after removal of condensable vapors) by passing this gas over a catalyst consisting of nickel oxide precipitated on a kieselguhr carrier and containing about 10% elemental nickel in oxide form. The temperature amounted to about 541 F. and the space velocity to about 151 cubic feet per cubic foot of catalyst volume per hour. The paraffin content of the gas was raised considerably, about 75% of the unsaturates being hydrogenated, and the gas was rendered absolutely interchangeable with natural gas.

Many details of construction and. procedure may be varied without departing from the principles of this invention, and it is therefore, not my intention to limit the patent granted on this invention otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

l. Apparatus for coking organic material comprising means defining a coking chamber adapted to have a layer of organic material spread over its floor, and a silicon carbide tube extending through the upper part of said chamber adapted to have fuel burned therein to generate heat to be radiated onto said layer of material for coking the same, said tube being permeable to gas so that carbonaceous deposits on said tube can be removed therefrom by establishment of outward gas flow through said tube walls.

2. Apparatus for coking organic material comprising means defining a coking chamber adapted tc have a layer of organic material spread over its noor, a silicon carbide tube extending through the upper part of said chamber adapted to have fuel burned therein to generate heat to be radiu ated onto said layer of material for coking the same, said tube being permeable to gas so that carbonaceous deposits on said tube can be removed therefrom by establishment of outward gas flow through said tube walls, means for introducing a fuel and air into said tube to bring about combustion therein, and means in the floor of said apparatus for effecting heat exchange between said air and combustion gases formed in said tube.

3. Apparatus for coking organic material comprising means defining a coking chamber adapted to have a layer of organic material spread over its floor, a plurality of spaced silicon carbide tubes extending through the upper part of said chamber adapted to have fuel burned therein to generate heat to be radiated onto said layer of material for coking the same, said tubes having porous walls so that carbonaceous deposits on said tubes can be removed therefrom by establishment of outward gas flow through said tube Walls, a plurality of spaced tubes receiving combustion gas from said carbide tubes and extending within the iloor of said apparatus, and a plurality of air tubes extending within said lowbetween said combustion gas tubes to preheat air passing through said air tubes, said air tubes discharging into said carbide tubes.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,811,621 Fairchild June 23, 1931 2,015,052 Hartley Sept. 17, 1935 2,343,866 Hincke Mar. 14, 1944 2,533,492 Mekler Dec. l2, 1950 

3. APPARATUS FOR COKING ORGANIC MATERIAL COMPRISING MEANS DEFINING A COKING CHAMBER ADAPTED TO HAVE A LAYER OF ORGANIC MATERIAL SPREAD OVER ITS FLOOR, A PLURALITY OF SPACED SILICON CARBIDE TUBES EXTENDING THROUGH THE UPPER PART OF SAID CHAMBER ADAPTED TO HAVE FUEL BURNED THEREIN TO GENERATE HEAT TO BE RADIATED ONTO SAID LAYER OF MATERIAL FOR COKING THE SAME, SAID TUBES HAVING POROUS WALLS SO THAT CARBONACEOUS DEPOSITS ON SAID TUBES CAN BE REMOVED THEREFROM BY ESTABLISHMENT OF OUTWARD GAS FLOW THROUGH SAID TUBE WALLS, A PLURALITY OF SPACED TUBES RECEIVING COMBUSTION GAS FROM SAID CARBIDE TUBES AND EXTENDING WITHIN THE FLOOR OF SAID APPARATUS, AND A PLURALITY OF AIR TUBES EXTENDING WITHIN SAID FLOW BETWEEN SAID COMBUSTION GAS TUBES TO PREHEAT AIR PASSING THROUGH SAID AIR TUBES, SAID AIR TUBES DISCHARGING INTO SAID CARBIDE TUBES. 